PSI - Issue 37

Dániel Antók et al. / Procedia Structural Integrity 37 (2022) 796–803 Dániel Antók, Tamás Fekete et. al. : Evaluation Framework … / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction The objective of Structural Integrity ( SI ) of large-scale, high-performance energy generating and chemical systems – with a particular focus on their pressure systems, called Large-Scale Pressure Systems ( LSPSs ) – is to assure the fail safe operation during their entire Service Lifetime ( SL ). The Design Service Lifetime ( DSL ) of an LSPS is the SL ‘ that the designer intends’ the system ‘ to achieve when subject to the expected service conditions … ’ Nireki (1996). DSL and expected service conditions are laid down in the design specification that serves as basis for the design. The DSL of an LSPS is justified by the Design Safety Calculations ( DSCs ) that simulate the long-term behaviour of the system, considering the effects of its expected load history. The Technically Allowable Lifetime ( TAL ) of a system is the time period – calculated from the start of its operation – , during which it can perform its intended functions safely, under normal working conditions and in case of various – very low probability, and mainly hypothetical – accidents. The expected TAL of these systems is predicted by Structural Integrity Calculations ( SICs ). SICs are computations that simulate the long-term behaviour of the systems by considering the combined effects of past actual operating history and expected future load history. Usually, for a system, D SL ≤ SL ≤ TAL . Supporting the safe operation of LSPSs for long-term operation ( LTO ) is a growing challenge for the scientific and engineering community, making the need to increase the accuracy of SICs ever more urgent. The efficacy of SICs is highly dependent on: (1) the predictive potential of the methodology’s underlying theoretical and numerical framework; (2) the amount and quality of information obtained from the material tests supporting the computations; (3) the amount and quality of information processed from materials testing results. Currently, long-term research is underway, at the Centre for Energy Research, Budapest, Hungary with the goal to establish an advanced methodology with increased predictive power for SI of LSPSs and bring it into industrial use. In this paper, for reasons of space limitations, the progress of an ongoing research focusing on questions of materials testing and their evaluation – in the framework of the Thematic Excellence Programme 2020 (2020-4.1.1.-TKP2020), in cooperation between the Centre for Energy Research and the University of Dunaújváros– is summarized in a nutshell. Results of the ongoing research are intended to be incorporated into – at least – the long-term project. 2. On the theoretical foundations of the Framework As mentioned in the introduction, DSCs for an LSPS are predictive computations that investigate the anticipated long-term behaviour and stability conditions of the system, considering the effects of the expected load history, to justify its DSL . DSCs cover both the examination of system’s structural stability – see Gilmore (1993) – and the stability of its structural materials – see Ivanova (1998) – . The stability analyses in DSCs are performed following the methodologies and rules prescribed by the corresponding design standards, e.g., ASME (2021). The roots of engineering standards defining the dimensioning methods and DSC methodologies for LSPSs date back to the turn of the 19 th and 20 th centuries. This is the rationale behind the fact that material models used in standards in force and used nowadays – e.g., ASME (2021) – are still almost exclusively linear , homogeneous , isotropic , and time-independent – see also Maugin (2009) – . Non-linear behaviour of the structural materials is approximated in current standards using oversimplified models. Since time constraints within an LSPS design project are always very tight, the DSC methodologies implement the simplest and fastest possible calculation methods that have been successfully applied so far. Standard-based calculations are made feasible by the standards themselves by providing appropriate input material properties for the dimensioning calculations and for the DSCs . The required material properties are derived from that of the results of material tests made (1) in compliance with standards for implementing and conducting the material tests – see ISO 6892-1 (2019) – , and then (2) evaluated in the spirit of the design standard – which is understood to be consistent with the material models used in it – . SICs for an LSPS are predictive computations that investigate its expected future behaviour and stability conditions, based: (1) on the information available when the calculations are performed, i.e. the ‘life history’ of the components (manufacturing, installation and operation/load history) and other relevant data (e.g. measured properties of structural materials, results of in-service inspections etc.); and (2) on the anticipated further operation/load history; to estimate its TAL . Stability examinations of an LSPS during SICs also cover both the system’s structural stability aspects and the stability aspects of its structural materials – see Gilmore (1993), Ivanova (1998) and Toribio (2020) – . In recent